(a) Field of the Invention
The present invention relates to a metronome, and more particularly to an improved structure of metronome that can accurately beat time at a low frequency.
(b) Description of the Prior Art
A regular metronome, as shown in FIG. 1, is generally comprised of a driving mechanism 1, an escapement wheel 2, an oscillating shaft 3, and an actuating member 40. The driving mechanism 1 is turned by the user to wind a spiral power spring 12, causing it to preserve energy for operating the metronome. When the spiral power spring 12 is released, a rotary force is applied to an escapement wheel 2, which has two staggered rows of sloping teeth 21 and 21' around its periphery. When the escapement wheel 2 is rotated, the actuating member 40 is forced to turn an axle 31 of an oscillating shaft 3 back and forth. The oscillating shaft 3 comprises a graduated pendulum bar 32 fixedly perpendicularly connected to one end of the axle 31, a fixed weight 34 at the bottom end of the pendulum bar 32, and a sliding weight 33 slidably mounted on the pendulum bar 32 above the elevation of the axle 31. The actuating member 40 (see FIG. 2) comprises a circular plate 401 having a peripheral notch 402 fitted with the sloping teeth 21 and 21' of the escapement wheel 2. When the escapement wheel 2 is rotated by the driving mechanism 1, the two staggered rows of sloping teeth 21 and 21' are moved with the escapement wheel 2 to pass through the peripheral notch 402 and to alternatively strike the circular plate 401 at two opposite sides of the peripheral notch 402, thereby causing the circular plate 401 to be turned back and forth. When adjusting the time beating frequency, the elevation of the sliding weight 33 is relatively adjusted. When the sliding weight 33 is adjusted upward toward the top limit position at the pendulum bar 32, the moment of arm is relatively increased, and therefore the oscillating speed of the pendulum bar 32 is relatively slowed down. On the contrary, when the sliding weight 33 is adjusted downwards toward the axle 31, the oscillating speed of the pendulum bar 32 is relatively accelerated. However, when the sliding weight 33 is adjusted to the top limit position at the pendulum bar 32, the pendulum bar 32 become unable to be effectively oscillated. Because the circular plate 401 of the actuating member 40 is a flat disk (see FIG. 3), no component of force is produced to push the circular plate 401 sideways when one sloping tooth 21 or 21' strikes the circular plate 401, and the sloping tooth 21 or 21' may pass through the peripheral notch 402 without touching one peripheral edge of the peripheral notch 402 at the circular plate 401 when the sliding weight 33 is adjusted to the top limit position at the pendulum bar 32.